To quantify the sequential changes in the metabolic response occurring in patients with end-stage liver disease after orthotopic liver transplantation (OLT). Detailed quantification of the changes in energy expenditure, body composition, and physiologic function that occur in patients after OLT has not been performed. Understanding these changes is essential for the optimal management of these patients. Fourteen patients who underwent OLT for end-stage liver disease had measurements of resting energy expenditure, body composition, and physiologic function immediately before surgery and 5, 10, 15, 30, 90, 180, and 360 days later. Resting energy expenditure was significantly elevated after surgery (24% above predicted), peaking around day 10 after OLT, when it averaged 42% above predicted. A significant degree of hypermetabolism was still present at 6 months, but at 12 months measured resting energy expenditure was close to predicted values. Before surgery, measured total body protein was 82% of estimated preillness total body protein. During the first 10 days after OLT, a further 1.0 kg (10%) of total body protein was lost, mostly from skeletal muscle. Only 54% of this loss was restored by 12 months. Significant overhydration of the fat-free body was seen before OLT, and it was still present 12 months later. Although significant losses of body fat and bone mineral occurred during the early postoperative period, only body fat stores were restored at 12 months. Both subjective fatigue score and voluntary hand grip strength improved rapidly after OLT to exceed preoperative levels at 3 months. At 12 months grip strength was close to values predicted for these patients when well. Respiratory muscle strength improved less markedly and was significantly lower than predicted normal levels at 12 months. Before surgery, these patients were significantly protein-depleted, overhydrated, and hypermetabolic. After surgery, the period of hypermetabolism was prolonged, restoration of body protein stores was gradual and incomplete, and respiratory muscle strength failed to reach expected normal values. Our measurements indicate that OLT does not normalize body composition and function and imply that a continuing metabolic stress persists for at least 12 months after surgery.